Synthetic rubber cure using a tetramethylol bis-phenol and product thereof



nits

y "No Drawing. Filed May 28, 1958, Ser. No. 738,321

, 19 Claims. (Cl. 260-415) This invention relates generally to thecuring of rubher and more particularly to the curing of syntheticrubbers by means of a particular class of curing agents. Still moreparticularly the invention relates to the curing of synthetic rubberswhereby the resulting cured product possesses the high tensile strengthobtainable by prior art curing systems but which possess enhancedelongation and resiliency over anything obtained in the prior art. Theinvention also relates to the resulting cured synthetic rubber. f

It is known to cure various synthetic rubbers with dimethylol. phenols.U.S. Patents Nos. 2,649,431 and 2,649,432, issued August 18, 1953,describe vulcanization procedures wherein certain dimethylol mononuclearphenols are used as vulcanizing'agents for a variety of syntheticrubbers. Similarly, US. Patents 2,701,895; 2,702,287; and 2,726,224 allteach the cure of butyl rubher with dimethylol phenols; these patentsalso. contain improvements in the art of curing butyl rubber with thedimethylol phenols alone.

Despite the excellence of the curing systems taught in theabove-described patents, particularly as applied to butyl rubber, thereis a need for a curing or vulcanizing system which will produce a curedrubber product having enhanced properties not obtainable by the patentedprocesses. It is the primary object of the present invention to supplysuch rubbers. It is a further object of the present invention to presenta method of curing synthetic rubbers rapidly and efiiciently to produce,useful products. These objects 'are accomplished in a surprisinglyefiective and straightforward manner. The invention contemplatesadmixing each 100 parts by weight of asynthetic rubber with 2-18 partsby weight of-a compound having the formul-a HO OH.

Dunc;

(HOCHz)? (CHQOH)! where n is a number from l-S, inclusive. The resultingmixture is then heated to a temperature in the range of about 2'OO400 F.to cure the rubber.

The synthetic rubbers which may be cured by the curing agents of thepresent invention include a wide variety of synthetic rubbers such asthe products known as 612$ (SBR) which is a copolymer of butadiene andstyrene containing about-50% to about 70% butadiene. There mayfalso beused the Buna Ns (NBR) whichare copolymers ofbutadiene and acrylonitrilecontaining about 50% to' about..80% butadiene. Generally speaking, theserubbers may be definedas polymersof aliphatic, conjugated diolefins andcopolymers, of aliphatic, conjugated diolefins with othercopolymerizable monomeric compounds. Thus homopolymers of butadiene (BR)may be employed 'asfwell ashomopolymers and/or copolymers of butadienehomologues such as isoprene. Neoprene (CR) may be used; neoprene is apolymer of 2-chlorobutadiene1,3, generally referred to as chloroprene.Butyl rubbers .(IIR) lend themselves to cures by the compounds of thepresent invention. Butyl rubber is the type of synthetic rubbermade bycopolymerizing as iso-olefin, usually iso butylene,.with a minorproportion of a multi-olefinic unsaturatehaving from 4 -l4 carbon atomsper molecule.

The iso-olefins used generally have from 4-7 carbonj atoms, and suchisomono-olefins as isobutylene or ethyl. The multi-olefinic un-v methylethylene are preferred. saturate usually is an aliphatic conjugateddiolefiin having from 4-6 carbon atoms, and is preferably isoprene orbutadiene. Other suitable dioleiins that may be mentioned are suchcompounds as piperylene; 2,3-dimethyl' butadiene-1,3; l-dimethylbutadiene-1,3; 1,3-dimethyl butadiene-1,3; 1,3-ethyl butadiene-1,3; and1,4-dimethyl butadiene-l,3. The butyl rubber contains only relativelysmall amounts of copolymeiized diene, typically from about 0.5-5%, andseldom more than 10%, on the total weight of the synthetic rubber.

The curing agents of the present invention to be added I to thesynthetic rubbers are all the reaction products of formaldehyde and abis-phenol; they will be the tetra-' methylol derivative of abis-phenol. Analysis sometimes indicates the presence of less than 4methylol groups per molecule, but this probably merely means that some'unreacted bis-phenol is present. Examples of the bis{ phenols which areto be reacted with the formaldehyde are bis-(4-hydroxy-phenyl) methane;bis-.(2-hydroxy- The reaction of the bis-phenol with formaldehyde iscarried out in the presence of a strong alkaline catalyst, especially analkali metal hydroxide, which is su-bse:

quently neutralized. Sufiicient formaldehyde is reacted with thebis-phenol to form the tetra-methylol compound. Thus the mole ratio offormaldehyde to bis-phenol will be slightly in excess of 4:1. Reactionis usually carried out in an aqueous medium. The mixture of thebis-phenol, formaldehyde, and alkaline catalyst is maintained at asuitably low temperature, for example, 25 40 C.. to preserve thetetra-methylol reaction product in the form of a monomer. Temperatureshigher than about 40 C. will produce some polymer which reduces theactivity of the compounds. The tetra-methylol bis-phe-. nols can beisolated by acidification of the reaction mixture and separation of thesolids or the oily layer. Water may be stripped from the mixture bywarming under vacuum. In view of the low temperatures of reactionnecessary to prepare the tetra-methylol compounds useful in the presentinvention, the period of time during.

which the reaction is carried out must be suficiently long tosubstantially completely consume all the formalde hyde. Depending on theprecise temperature within the limits stated above, reaction time mayvary from two hours to several days.

The final tetra-methylol bis-phenol will generally initially be preparedin the form of an oil. This oil, how: ever, is readily converted to asolid by removing any free formaldehyde from the system chemically or bythorough washing. It has been found in practice that once the oilyproduct has been converted to a solid, sub sequent runs in the sameequipment produce the tetramethylol' bis-phenols as solid products morereadily. This is apparently due at least in part to fortuitous seed-Iing of the product; such seeding occurs even after the equipment hasbeen thoroughly cleaned. I The tetra-methylol bis-phenol is used inamounts of about 1 to 18 parts by weight to parts by Weight of the butylrubber. There will generally be added catalytic amounts or" substancesto speed the reaction between the rubber and the tetra-methylolbis-phenol. The catalysts will generally be acidic in nature. Organicacids such as acetic acid and benzoic acid may be used. Additionally,the organic sulfonic acids such as para-toluene sulfonic acid,

Patented Sept. 19, 1961 3 phenol-hydrazine sulfonic acid, and ethanesulfonic acid are all suitable for shortening the cure time. Anotherclass of compounds suitable for accelerating the reaction between therubbers and the tetra-methylol bis-phenol are the heavy metal halides asset forth in aforesaid US. Patent 2,726,224. Examples of the stableacidic halides are tin chlorides, zinc chloride, iron chlorides, and ingeneral the halides of the various metals usually classified as heavymetals, including the chlorides of aluminum, chromium, nickel, cobalt,manganese, and copper. The accelerators are used in amounts of about0.2-5 parts by Weight accelerator per 100 parts by weight rubber.

The mixing of the ingredients is carried out by known methods. Therubber, the tetra-methylol bis-phenol, the accelerator, and anyadditional desired ingredients may be mixed together in any desiredorder according to the procedures ordinarily used in mixing rubbercompounds with the aid of the usual rubber-mixing equipment such as aninternal mixer or roll mills. For many purposes there will generally beincluded in the mixture a quantity of a suitable reinforcing material,preferably carbon black. The amount of carbon black to be used will varyaccording to the properties of the f nished product desired, but therewill generally be used 20-100. parts by weight carbon black per 100parts by weight rubber, and more preferably 4080 parts black, and mostpreferably 50-60 parts by weight black per 100 parts rubber. Othercompounding ingredients such as additional fillers, processing aids, andthe like may be included in the mixture if desired. Some compositionssuch as rubber tile for flooring may contain a mixture of mineralfillers, including both fibrous and nonfibrous fillers, additionalresins to impart special properties, certain plasticizers and pigmentsto impart the desired color.

The curing processes to be applied to the compcsi-. tion of the presentinvention are thosegenerally used curing processes known in the rubberart. The'temperat'fi'res to be used will be those in excess of 200 F.and preferably in excess of 300 F. for periods of time ranging from fiveminutes to three hours, the longer periods of time within the statedtime range being employed with the lower temperatures. The broadtemperature range will be 200-400 F. while the preferred vulcanizingtemperatures are within the range of about 320 F. to 370 F. Temperaturesnear the upper limits should not be employed for a sufficiently longtime to cause thermal injury to the article being cured.

"Initial cure of butyl rubbers with the curing agents of the presentinvention will produce vulcanized rubber ha ing fair tensile strengthand good elongation. However, on aging the vulcanized butyl rubberproducts, for example, aging for one week at a temperature of about 300F., the tensile strengths of the products. will greatly improve whilemaintaining the excellent elongation. The final product will thuspossess tensile strengths comparable to those achieved by the prior art,but with greatly improved elongation.

The 'vulcanizable mixture resulting from the admixing of theabove-describedingredients may be fabricated into the desired form bythe usual methods such as calendering, extrusion, or molding andsubsequently vulcanized by heating preferably while confined underpressure. Use of the tetra-methylol bis-phenol compounds in the rubbercompositions as contrasted with use of the dimethylol phenols of the.prior art will allow preparation of the composition without as muchdanger. of scorching during the mixing steps on a mill or internalmixer. j

The following examples illustrate several embodiments of the invention.All parts are by weight unless otherwise stated.

Example 1 Into a stainless steel container containing 800 partsof 10%aqueous sodium hydroxide solution (2 mols NaOl-l) was introduced 228parts (1 mol) 2,2-bis-(4-hydroxyphenyl) propane. The temperature rose to30-35 C. After cooling to room temperature (about 28 C.), there wasadded 330 parts (4.4 mols) 40% solution of formaldehyde. The mixture wasallowed to stand .at room temperature for 24 hours. 2

At'the end of that period, the mixture was acidified with a 30% solutionof acetic acid to a pH of 6. The bottom oily layer was separated andwashed thoroughly with water. The tetra-methylol derivative of2,2-bis-(4- hydroxy-phenyl) propane crystallized to form a creamy whitesolid. This 2,2-bis-(3,5-dimethylol, 4-hydroxyphenyl) propane was usedin the examples below where indicated under the name tetra-methylolbis-phenol.".

Example 11 A master batch was prepared of relative proportions of partsof a butyl rubber designated as Butyl 365,?

50 parts of HAF carbon black (Philblack O), i part stearic acid, and 3parts staunous chloride. Mixing was carried out on a mill in the usualmanner.

Of the master batch 154 parts were blended on a mill" with 7.5 parts ofthe tetra-methylol bis-phenol prepared as described in Example 1. Afterthorough dispersion of the tetra-methylol compound, the mixture wassheeted olf the mill and press cured at 320 F. Difierent specimens werecured for dififerent lengths of time. Following are the results: 5

. Tensile Hardness, Elongation, Minutes creme Strength, Shore A PercentLbs/sq. in.

1, 695 66 3&0

No difficulty with scorching was encountered in prepa ration of themaster batch or the final mix. The above specimens were aged for oneweek in an air-circulating oven maintained at 300 F. Following are theresults:

Minutes of Initial ours Tensile Hardness, Elongation,

Strength Shore A Percent 1, s50 at 270 1, no 67 290 1,460 as 290 When154 parts of the master batch was admixed with 7.5 parts of a compoundwhich is a dimethylol phenol instead of a tetra-methylol bis-phenol,tensile strengths of the cured final product were slightly higher thanthose given above before aging, but the Shore A hardness was slightlylower. Additionally, the mixture tended to scorch on the mill.

Example III A rubber tile formulation was prepared by the usual mixingtechnics. Following is the formula:

tile was-sheeted out fto 0.'1 25" in'thickness and press cured for nineminutes at atemperature of 327 F.; Anexccllenttileresulted. 1 The aboveformula is substantially identical to that used in rubb'ertile formulasave that the ,tetra-methylol bis-phenol compound hasbeemsubstitute'dfor the conventional .curing system of sulfur, zinc oxide, magnesiumoxide, and accelerator The curing of the 'tile'with the tetra-'methylolbis-phenol compound produced a white'r tile than was possible with-acomposition containing a sulfur curing system. Y Y 1 When the aboveformula was repeated using a -dimethylol phenol instead of thetetra-methylol bis-phenol, no substantial cure resulted. Three separatecompositions were prepared containing-respectively, (l) 2,6- dimethylol,4-o'ctyl phenol (Amberol ST-137); (2) a dimethylol phenol resin(Catalin9273), and (3) a dimethyl phenol resin (Schenectady SP-1045).The resulting products were unsuitable-as floor coverings since they hadinsuflicient cure.

Example IV The follovi'ingv composition was prepared: d e V PartsButadiene-styrene copolymer (GR-S '1502) I 10.0

Oil-soluble sulphonic acids in parafiin oil (Rco- ITletra-methy'lol'bis-phetiOLL... Stannous chloride Stearic acid"; .1 The copolymer,peptizingagent, channel black, tetramethylol bis-phenol, and stearicacid were admixed on a mill and heated to a temperature in'the range of225 235 F. until thorough mixingwas accomplished. The mix was thencooled and there was" added the P--33 black; the process oil, and thestannous chloride on the cold mill until thorough mixing wasaccomplished. The mixture was then sheeted off and cured at 300 F. for20 minutes in a press. An excellent, strong, flexible rubber sheetresulted.

When the example was repeated using natural rubber instead of thebutadiene-styrene copolymer, no substantial cure resulted.

Example V The following formulation was mixed similarly to Example IV:Ingredients: Parts Butadiene-acrylonitrile copolymer, 33% acrylonitrile(Hycar 1042) 100 Stearic acid 1 Carbon black (l -33) 30 Channel black(EPC) l5 Dibutyl phthalate 12 Cumar-indene resin (MH 2 /2) 12Tetra-methylol bis-phenol 7.5 Stannous chloride 3 Some slight curing wasnoted on the mill. The mixture was sheeted oil and cured for minutes at320 F. A strong, flexible rubber sheet resulted.

Example VI The following mixture was cold mixed on a cold mill:Ingredients: Parts Polychloroprene (Neoprene W) 100 Carbon black (P-33)Channel black (EPC) 15 Light oil 8 Tetra-methylol bis-phenol 7.5Stannous chloride 3 Channel black (ERC) 15 Carbon bla'ck (P43) 30 Lightoil a- 8 Tetra-methylol -bis-phen0l; ..7."5 Stannouschloride 3 the milland cured for '20' F. A strong, tough, flexible rubber" The mixture wassheeted off minutes at 320 product resulted.

Example VIII The following ingredients were mill mixed:

Ingredients: r I Parts" Butyl rubber (Butyl 365) 1'00 Philblack O 50Stearic acid -.L'. 1.0 Tetra methylol bis (4 'hydroxyl phenyl) methane7.5 Stannous chloride.. 2.0

i The mixture was sheeted off the mill and cured for 20 minutes at 320F.

A strong, tough, flexible rubber. product resulted. lclaimr l 1. Themethod of curing a synthetic rubber selected from the group'consistingof butadiene-styrenecopolymers, butadiene-acrylonitrile copolymers,copolymers ofisobutylene with a minor proportion of a multi-olefinicunsaturate having from 4-14 carbon atoms. per molecule; polychloroprene,and chlorosulfonated polyethylene which comprises admixingwith eachparts by weight of said synthetic rubber 2-18 parts by weight of.acompound having the formula (HO CH2): (CHeOHh where n is a number froml-S, inclusive, and heating the mixture to a temperature in the range of200400 F. to cure the rubber.

2. The method according to claim 1 wherein said compound is present inan amount of about 7-8 parts by weight per 100 parts by weight of saidrubber.

3. The method according to claim 1 wherein n is 3.

4. The method according to claim 1 wherein n is 1.

5. The method according to claim 1 wherein said heating is carried outat a temperature of about 320 F.

6. The method according to claim 1 including the step of incorporatingcarbon black into said mixture.

7. The method according to claim 1 wherein said synthetic rubbercomprises a butadiene-styrene copolymer.

8. The method according to claim 1 wherein said synthetic rubbercomprises a butadiene-acrylonitrile c0- polymer.

9. The method according to claim 1 wherein said synthetic rubbercomprises a copolymer of isobutylene with a minor proportion of amulti-olefinic unsaturate having from 4-14 carbon atoms per molecule.

10. The method according to claim 1 wherein said synthetic rubbercomprises a polychloroprene.

11. The method according to claim 1 wherein said synthetic rubbercomprises a chlorosulfonated polyethylene.

12. The method according to claim 1 wherein an organic acidic catalystis admixed with said rubber and said compound.

13. A vulcanizable composition of matter comprising relative proportionsof 100 parts by weight synthetic rubber selected from the groupconsisting of butadienestyrene copolymers, butadiene-acrylonitrilecopolymers,

copolymers of isobutyleue with a minor proportion of a multi-olefinicunsaturate having from 4-14 carbon atoms per molecule, polychloroprene,and chlorosulfonated polyethylene and 2-18 parts by weight of a compoundhaving the formula HO OH (HUGHI)! (CHIOH)1 wherein n is a number from1-5, inclusive.

14. An elastic vulcanizate comprising a synthetic rubber selected fromthe group consisting of butadienestyrene copolymers,butadiene-acrylonitrile copolymers, copolymers of isobutylene with aminor proportion of a multi-olefinic unsaturate having from 4-14 carbonatoms per molecule, polychloroprene, and chlorosulfonated polyethylenevulcanized with-from 2-18 parts by weight per 100 parts by weight ofsaid rubber of a compound having the, formula HO OH 13003:): (CHzOH):

where n is a number from l-S, inclusive.

"15. A vnlcanizate according to claim 14 containing ethylene, mineralfillers therefor, and Pigments, incorporating into the mixture. about.2-18 par s by weight. per parts by weight of'said synthetic rubber of ac mpound having he touuula (HOGHa): (CHQOH): wherein n is a number from1-5, inclusive, forming a sheet-trout the resulting mixture, and curingsaid sheet at a temperature in the range of about 200-400 F.

19. A vulcanized rubber flooring composition comprising a syntheticrubber selected from the group consisting of butadicne-styrenecopolymers, butadieue acrylonitrile copolyrners, copolymers ofisobutylene with a minor proportion of a multi-olefinic unsaturatehaving from 4 14 carbon atoms per molecule, polychloroprene, andchlorosulfonated polyethylene and mineral fillers therefor, vulcanizedwith from 2-18 parts by weight per 100 parts by weight of said rubber ofa compound having;

the formula HO OH OGnHn'K V (no on), (03,011),

wherein n is a number from l-S, inclusive.

References Cited in the file of this patent UNITED STATES PATENTS Dec.6, 1955 OTHER REFERENCES Carswell: Phenoplasts," page 10, 1947,Interscience Publishers, Inc, New York.

13. A VULCANIZABLE COMPOSITION OF MATTER COMPRISING RELATIVE PROPORTIONSOF 100 PARTS BY WEIGHT SYNTHETIC RUBBER SELECTED FROM THE GROUPCONSISTING OF BUTADIENESTYRENE COPOLYMERS, BUTADIENE-ACRYLONITRILECOPOLYMERS, COPOLYMERS OF ISOBUTYLENE WITH A MINOR PROPORTION OF AMULTI-OLEFINIC UNSATURATE HAVING FROM 4-14 CARBON ATOMS PER MOLECULE,POLYCHLOROPRENE, AND CHLOROSULFONATED POLYETHYLENE AND 2-18 PARTS BYWEIGHT OF A COMPOUND HAVING THE FORMULA
 19. A VULCANIZED RUBBER FLOORINGCOMPOSITION COMPRISING A SYNTHETIC RUBBER SELECTED FROM THE GROUPCONSISTING OF BUTADIENE-STYRENE COMPOLYMERS, BUTADIENE-ACRYLONITRILECOPOLYMERS, COPOLYMERS OF ISOBUTYLENE WITH A MINOR PROPORTION OF AMULTI-OLEFINIC UNSATURATE HAVING FROM 4-14 CARBON ATOMS PER MOLECULE,POLYCHLOROPRENE, AND CHLOROSULFONATED POLYETHYLENE AND MINERAL FILLERSTHEREFOR, VULCANIZED WITH FROM 2-18 PARTS BY WEIGHT PER 100 PARTS BYWEIGHT OF SAID RUBBER OF A COMPOUND HAVING THE FORMULA